1. Field of the Invention
The present invention belongs to the technical field of extrusion molding and relates to an extrusion molding machine by which a molten resin material is extruded through a die by an extruder and further extruded through a pair of delivery rolls.
2. Description of the Related Art
As shown in FIG. 11, a molding part 610 in a conventional molding machine is provided with a pair of upper and lower delivery rolls 601 supported by a frame 605, and a rolling part 607 between this pair of delivery rolls 601 is arranged before a die 602 installed at the end of an extruding machine 4.
Upon extrusion of a molten resin material in a cylinder 42 by rotating a screw 41 in the extruder 4, the molten resin material is passed through a resin flow path 621 in the die 602 and extruded from the discharge opening at the end of the die 602, and by rotating a pair of the delivery rolls 601, the molten resin material extruded toward the rolling part 607 between the delivery rolls 601 is delivered from the delivery part 608 at the opposite side of the rolling part 607 to form a product sheet S. The molten resin material is molded in this manner into the product sheet S by the extrusion molding machine equipped with a pair of the delivery rolls 601.
As the molten resin material, various thermoplastic resins and rubber materials are used. A lubricant is added to this molten resin material to improve the releasability of the product sheet S from the delivery rolls 601, a foaming agent is added in foaming molding, and various additives are incorporated depending on molding processability and characteristics of moldings.
Since the rolling part 607 between a pair of the delivery rolls 601 is open, the molten resin material extruded from the die 602 is exposed immediately to atmospheric pressure. Accordingly, there Is a problem that a part of the compounding ingredients in this molten resin is diffused into the atmosphere.
For example, when a molten resin material containing a foaming agent is used in foaming molding, there is a problem that upon extrusion of the molten resin material containing a foaming agent from the die 602, the melting viscosity of the molten resin material is low so that the gas in the resin material cannot be maintained in the resin material, thus diffusing into the atmosphere, breaking bubbles and roughing the surface of the product to worsen the outward appearance.
Further, when highly volatile compounding ingredients are contained, a part of the volatile compounding ingredients is evaporated upon extrusion of the molten resin material from the die 602. If such evaporated volatile compounding ingredients are, for example, a lubricant added for improving releasability from the delivery rolls 601, the release of the product sheet S from the delivery rolls 601 is deteriorated to worsen the surface conditions of the delivered product sheet S.
The object of the present invention is to prevent diffusion etc. of compounding ingredients in a molten resin material upon extrusion of the molten resin material from a die in xe2x80x9ca molding extrusion machine comprising a pair of delivery rolls arranged forward continuously with a die attached to the end of an extruder by which a molten resin material is extruded through the die toward a rolling part between the delivery rolls and further extruded through a pair of the delivery rollsxe2x80x9d.
The technical means taken for solving the problem described above are as follows:
xe2x80x9cGas-sealing molds in intimate contact with both sides at least at the top of the die at the side of the discharge opening are provided to close openings in both sides of the rolling part so that supporting parts in both sides of a pair of the delivery rolls are formed into an air-tightness keeping part by said gas-sealing molds.xe2x80x9d
The technical means described above act as follows.
The gas-sealing molds are provided in intimate contact with both sides at least at the top of the die at the side of the discharge opening thereby closing openings in both sides of the rolling part, so that the space in the rolling part between the delivery rolls is closed by the gas-sealing molds and the die. Further, the supporting parts for a pair of the delivery rolls are formed into an air-tightness keeping part by said gas-sealing molds, so that in both sides of the delivery rolls, the gas-sealing between the delivery roll and the gas-sealing mold is achieved by said gas-tightness keeping part.
Therefore, upon extrusion of the molten resin material out of the die, the rolling part is highly airtight to form a high-pressure zone kept at high pressure. Accordingly, the molten resin material extruded out of the die can be maintained at high pressure even in the rolling part.
Another technical means is xe2x80x9cthe die is intimately and externally fitted with gas-sealing molds being open forward, a pair of the delivery rolls is accommodated in the gas-sealing molds, and supporting parts in both sides of a pair of the delivery rolls are formed into an air-tightness keeping part by said gas-sealing molds.xe2x80x9d
In this case, a pair of the delivery rolls is accommodated in the gas-sealing molds with which the die is intimately and externally fitted, and thus the space in the rolling part between the delivery rolls is closed by the gas-sealing molds and the die. In this case too, the supporting portions in both sides of a pair of the delivery rolls are formed into a gas-tightness keeping portion, so that in both sides of the delivery rolls, the gas-sealing between the delivery roll and the gas-sealing mold is achieved by said gas-tightness keeping part. By this constitution, the space in the rolling part is rendered highly airtight.
In this case too, therefore, the molten resin material is extruded from the die thereby reducing the leakage, out of the highly airtight rolling part, of the air and volatile components and a foaming agent etc. for foaming molding, to achieve a high-pressure zone kept at atmospheric pressure or more. By this constitution, the molten resin material extruded from the die is pressurized at atmospheric pressure or more, even in the rolling part. That is, the molten resin material is kept at atmospheric pressure or more until it is formed into a product sheet by delivery with a pair of the delivery rolls.
Said gas-tightness keeping part is constituted by xe2x80x9cinterposing an O-ring in a freely rotating part between the rotating shaft of each of the delivery rolls and the gas-sealing mold.xe2x80x9d
In each of the technical means wherein xe2x80x9csaid gas-tightness keeping part comprises resin packing interposed inside of the O-ringxe2x80x9d, the gas sealability between the delivery roll and the gas-sealing mold can be further improved. In addition, even if a part of the molten resin material extruded from the die permeates into the supporting parts at both sides of the delivery rolls, the molten resin material is sealed by the resin packing thereby preventing the leakage of the molten resin material from the gas-sealing molds.
In each of the technical means wherein xe2x80x9csaid die is thinning toward its top along the rolling faces of the delivery rolls, and the top is inserted into the rolling part with a gap therebetween to prevent the top from contacting with the rolling facexe2x80x9d, the air-tightness of the space in the rolling part can be further improved by the thinning part of the die, and the maintenance of the high pressure in the rolling part as the high-pressure zone can be further improved.
In each of the technical means wherein xe2x80x9cat least one member of the delivery roll, the die and the gas-sealing mold has a temperature-regulating functionxe2x80x9d, not only the viscosity of the extruded molten resin material but also the surface temperature of the extruded molten resin material can be regulated thereby preventing disruption of foams more effectively, to provide a product with a good appearance.
In each of the technical means wherein xe2x80x9ca pair of the delivery rolls is delivery rolls rotated by a rotation driving means connected to at least one of the delivery rolls, and the rotation of the delivery rolls is regulated by the rotation driving means to limit the discharge, from the delivery rolls, of the molten resin material extruded through the diexe2x80x9d, the amount of the molten resin material as the bank in the rolling part is increased and thus the pressure of the high-pressure zone can be maintained at higher pressure.
In each of the technical means wherein xe2x80x9cthe gap between the top of the die and the rolling face of the delivery roll is set to be an interval which permits the molten resin material extruded from the die to permeate into the gap and remain thereinxe2x80x9d, the molten resin material having permeated into the gap prevents the leakage, through the gap, of the air and volatile components or a foaming agent etc. in foaming molding, thus further improving the air-tightness of the space in the rolling part.
In each of the technical means wherein xe2x80x9cthe gap between the top of the die and the rolling face of a pair of the delivery rolls is set to be an interval which is not greater than 4 mmxe2x80x9d, the remaining amount, being in trouble, of the melted resin material in the gap can be further reduced by setting the gap between the top of the die and the rolling face of a pair of the delivery rolls to be a relatively small clearance which is not greater than 4 mm. Thereby, rotating the rolls is conducted smoothly, and further turbulence of the molten resin material""s streaming such as its counter-streaming into the gap is reduced.
In addition, it is preferable that the gap is set to be not greater than 3 mm. More preferred is not greater than 2 mm, further preferred is not greater than 1 mm. That is to say, the smaller a clearance in the gap becomes, the more the remaining amount of the molten resin material in the gap and the turbulence of the molten resin material is reduced.
As regards the above-described extrusion molding machine, in a case of forming molding, it is possible to manufacture products with a good appearance showing no uneven distribution of foams and uniform shape of foams in the products because the turbulence of the molten resin material""s streaming caused by its counter-streaming into the gap is reduced.
In each of the technical means wherein xe2x80x9csaid die is thinning toward its top along the rolling faces of the delivery rolls, and the top is inserted into the rolling part with a gap therebetween to prevent the top from contacting with the rolling facexe2x80x9d, the molten resin material extruded through the die is immediately delivered by rotation of a pair of the delivery rolls because a discharge opening of the die is brought near to a rolling part between a pair of the delivery rolls. Due to that, the remaining amount, being in trouble, of the molten resin material in the gap and turbulence of the molten resin material""s streaming into the gap caused by its counter-streaming into the gap are further reduced.
As described above, the melted resin material extruded toward the side of the rolling part as the high-pressure zone between the delivery rolls is kept at high pressure thereby preventing the diffusion etc., from the rolling part, of the compounding ingredients in the melted resin material.
Particularly in foaming molding, it is possible to control the diffusion, into the atmosphere, of the gas in the molten resin material in the rolling part, thus preventing occurrence of ruptured foams as a cause of an inferior appearance of the product.
In addition, when a volatile lubricant is contained in the molten resin material, the lubricant as a volatile component can be prevented from being evaporated in the rolling part, and thus reliably releasing the product sheet from the delivery rolls can be conducted.
Moreover, not only the remaining amount of the molten resin material in the gap between the top of the die and the rolling face of a pair of the delivery rolls but also turbulence of the molten resin material""s streaming such as its counter-streaming into the gap is reduced, thereby delivery of products is conducted smoothly without any poor appearance. Particularly in forming molding, it is possible to manufacture products with a good appearance showing no uneven distribution of foams and uniform shape of foams in the products because the turbulence of the molten resin material""s streaming caused by its counter-streaming into the gap is reduced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.